Chapter 7: Skeletal System Flashcards
Four Classes of Bones
long, short, flat, irregular (*sesamoid)
Long Bones
have longitudinal axes and expanded ends (allow for greater efficiency)
Examples: radius, ulna, femur, tibia, fibula.
Short Bones
cube-like
Examples: carpals and tarsals
Flat Bones
plate-like with broad surfaces
Examples: skull, ribs, and scapula
Irregular Bones
various shapes
Examples: vertebrae and facial bones
Sesamoid Bones
round bones that are small and nodular and embedded with tendons by joints.
Example: patella (kneecap)
Parts of Long Bone
Epiphysis, Articular Cartilage, Diaphysis, Periosteum, Processes, Medullary Cavity, Endosteum, Marrow
Epiphysis
expanded portion of the long bone which articulates (meets) with another bone.
made of spongy bone - which has bony plates called trabeculae
Articular Cartilage
hyaline cartilage that coats the articulating part of the epiphysis.
articulate: where it meets with something else
Diaphysis
shaft of the long bone between epiphysis.
wall of diaphysis is compact bone which has a continuous extracelllular matrix with no gaps
Periosteum
tough, vascular, fibrous membrane that covers the diaphysis of the bone.
functions to form and repair bone tissue
Processes
provides site for attachments of tendons or ligaments
Bones usually have compact bone overlying spongy bone
none
Medullary Cavity
runs through the diaphysis which is semi-rigid tube with a hollow chamber.
Endosteum
lines the cavity and the spaces of spongy bone and contains bone-forming cells
Marrow
the tissue that fills the spaces of the bone
red & yellow
Microscopic Structure of Bone
osteocytes: bone cells located in tiny, bony chambers called lacunae, which form concentric circles around central canals (Haversian canals)
function: transport nutrients (calcium/inorganic salts) and waste (worn out cells) to & from nearby cells
cell processes of osteocytes pass through canaliculi
extracellular matrix is composed of collagen and inorganic salts which gives bones strength and resilience
Compact Bone
osteon: cylinder shaped unit of compact bone.
many osteons cemented together forms the substance of compact bone
each central canal contains BV and nerves
perforating canals (Volkmann’s canals) connect central canals and contain larger BV and nerves
Spongy Bone
composed of osteocytes and extracellular matrix
bone cells lie within trabeculae and get nutrients from substances diffusing into the canaliculi that lead to thin, bony plates
Bone Development & Growth
parts of the skeleton begin to form during the first few weeks of prenatal development
bones form by replacing existing CT
bones continue to grow and develop into adulthood
intramembranous bones originate within sheetlike layers of CT
endochondral bones begin as masses of cartilage that are later replaced by bone tissue
Intramembranous Bones
broad, flat bones of the skull
during osteogenesis, membrane-like layers of unspecialized CT appear at the sites of future bones
dense BV supply the CT layers with nutrients so they can continue to grow
the cells then enlarge & become further differentiated (more defined) into osteoblasts (bone forming cells)
osteoblasts then deposit bony matrix around themselves
as a result spongy bone forms in all directions along the BV within the CT
later, some spongy bone becomes compact bone as spaces fill with bony matrix
as development continues, osteoblasts may become surrounded by matrix and become secluded within lacunae
that matrix encloses the processes of osteoblasts and gives rise to canaliculi
once those are isolated, the osteoblasts become osteocytes.
Endochondral Bones
most skeletal bones are endochondral bones
develop from masses of hyaline cartilage
the surrounding matrix breaks down and soon the cartilage cells die and degenerate. As it decomposes, periosteum forms from CT then encircles structure.
osteoblasts form spongy bone in the space occupied by cartilage.
osteoblasts become osteocytes when the bony matrix completely surrounds them. Then they’re called osteocytes
osteoblasts beneath the periosteum (tissue that surround bone) deposit compact bone around spongy bone.
Primary Ossification Center
occurs when in uterus.
when bony tissue replaces hyaline cartilage int he center of diaphysis.
the epiphysis of developing bone remains cartilaginous and continue to grow.
Secondary Ossification Center
towards the end
this appears later in the epiphyses and spongy bone forms in all directions
as it is deposited in both the diaphysis and epiphysis a band of cartilage forms called epiphyseal plate (growth plate) and remains between ossification centers.
Growth of Epiphyseal Plate
cartilaginous cells of epiphyseal plate forms 4 layers
- (innermost/deepest layer) (deep to superficial) anchors the epiphyseal plate to bony tissue of the epiphysis (closest to end of epiphysis and the cells do not participate in growth)
- rows of many young cells undergoing mitosis (cell division). the cartilaginous plate thickens as new cells appear.
- (thickest layer because it’s where both old and new cells are occupying space) formed by older cells which are left behind as new cells appear and those enlarge and thicken the epiphyseal plate, which lengthens the bone.
- composed of dead cells & calcified extracellular matrix (thin layer)
Osteoclasts
osteoclasts break down the calcified matrix
also phagocytize parts of the bony matrix
after osteoclasts remove the extracellular matrix, osteoblasts deposit bone tissue in place of the calcified cartilage.
long bones lengthen while cartilaginous cells are active
once ossification centers of the diaphysis and epiphysis meet, the plates close and growth is not possible.
over the course of your life, osteoclasts resorb bone tissue and osteoblasts replace bone.
Factors That Affect Bone Development, Growth, and Repair
nutrition, hormonal secretions, physical stress
Nutrition
vitamin D to absorb calcium (received through UV light)
vitamin A for osteoblast & osteoclast activity
vitamin C for collagen synthesis
Hormonal Secretions
growth hormone: stimulates division of cartilage cells in epiphyseal paltes
parathyroid hormone: stimulates increase in number & activity of osteoclasts
sex hormones: promote formation of bone tissue
- females reach maximum heights earlier due to estrogen effects on epiphyseal plates are stronger than testosterone
Physical Stress
stimulates bone growth: Wolff’s Law
Central Canal
tiny channel in bone tissue that contains a blood vessel; Haversian canal; tube within the spinal cord that is continuous with the ventricles of cerebrospinal fluid.
Haversian Canal
proper name for central canal
Canaliculi
only found in compact bone
microscopic canal that connects lacunae of bone tissue
Osteocyte
mature bone cell
Osteoclast
cell that erodes bone
Osteoblast
bone-forming cell
Osteon
cylinder-shaped unit containing bone cells that surround a central canal; Haversian system.
Bone Function
gives shape to structures
support body weight
- lower limbs, pelvis, vertebral column
protect organs
- eyes, ears, brain, lungs, abdominal, internal reproductive organs
blood cell formation
- begins in the yolk sac in embryonic development
- later are made in liver, spleen, bone marrow.
Marrow
soft netlike mass of CT within the medullary cavitites, irregular spaces of spongy bone, and central canals of compact bone.
Red Marrow
functions in forming RBC, WBC, and platelets
- occupies cavities of most bones in infants
- as adults, found in spongy bone of skull, ribs, sternum, clavicles, vertebrae, and pelvis
Yellow Marrow
as we age, yellow marrow replaces red marrow
yellow marrow stores fat
